This invention relates to a fluorescent display device and a process for manufacturing the same, and more particularly to a fluorescent display device having a planar cathode incorporated therein and a process for manufacturing the same.
In general, a fluorescent display device includes a box-line envelope of which an interior is evacuated to a high vacuum. The envelope is provided therein with a cathode acting as an electron source, a control electrode, and an anode having a phosphor deposited thereon so as to serve as a luminous display section. In the conventional fluorescent display device thus constructed, electrons emitted from the cathode are caused to selectively impinge on the phosphor while being controlled by the control electrode, so that the phosphor is selectively excited, resulting in a desired luminous display being carried out.
Recently, a planar cathode such as a field emission cathode (hereinafter referred to as "FEC") has been often used as a cathode for the fluorescent display device in place of a filamentary cathode. A typical spindt-type FEC includes an insulating layer and a gate electrode which are laminatedly formed on a cathode conductor of a cathode substrate. The insulating layer and gate electrode each are formed with a number of holes extending to the cathode conductor. The holes each are provided therein with an emitter of a conical shape in a manner to be positioned on the cathode conductor. Then, application of a voltage of a suitable level to each of the emitters and the gate electrode causes electrons to be emitted from the emitter.
The planar cathode such as an FEC or the like permits emission of electrons therefrom to be directly controlled by means of a voltage applied thereto. Thus, when the planar cathode is used as an electron source for the fluorescent display device, it is required that the cathode substrate on which the planar cathode is provided is arranged in proximity to the anode substrate on which the phosphor layer is deposited, to thereby prevent electron beams from spreading before they reach the anode. Also, when the phosphor is deposited in a strip-like or dot-like manner on the anode, it is required to align the phosphor layer of the anode with the cathode. This permits only control of the planar cathode to directly control a luminous display of the anode.
The conventional fluorescent display device includes a getter which is arranged so as to absorb residual gas thereon, to thereby permit the envelope to be evacuated to a high vacuum. Unfortunately, in order to accomplish this purpose, it is required to maintain, in the envelope, a space for arranging the getter. Thus, the conventional fluorescent display device, as shown in FIG. 6, is typically constructed in such a manner that an envelope 101 and a cathode substrate 100 are provided separate from each other, resulting in an interval between an anode 103 and a cathode 104 being adjusted depending on a thickness of the cathode substrate 100. Also, alignment between the anode 103 and the cathode 104 is carried out by previously positioning the cathode substrate 101 on one of front and rear plate members constituting the envelope 101 and then positioning the cathode substrate 100 with respect to the other plate member on which the anode 103 is formed.
In the conventional fluorescent display device thus constructed, the envelope 101 is formed by assembling the plate members by means of a sealing agent or material such as low-melting frit glass deposited on each of the plate members, fixing the plate members to each other by vertically applying a pressure thereto while interposedly holding them by means of a clip or the like, and subjecting the plate members to a heat treatment or calcination to melt the sealing material, resulting in the plate members being integrally connected to each other.
Thus, the envelope 101 is pressurized by the clip or the like which interposedly holds it, so that profile irregularity of side plates 102 of the envelope 101 causes misregistration between the plate members to occur during assembling of the envelope 101, resulting in alignment between the anode 103 and the cathode 104 in a horizontal direction being rendered highly difficult. Concurrently, profile irregularity of the side plates 102 requires to provide the interval between the anode 103 and the cathode 104 with allowance, thus, it is impossible to position the front and rear plate members in close proximity to each other and with high precision.
Further, in the conventional fluorescent display device, the envelope 101 is typically made of a glass plate. Also, the cathode plate 100 is often made of Si in the case that a drive circuit for the cathode 103 is formed on the cathode substrate 100. In this instance, when the fluorescent display device is so constructed that the cathode substrate 100 is mounted on one of the front and rear plate members of the envelope 101 in such a manner as conventionally employed in the art, a different in thermal expansion coefficient between the cathode substrate 100 and the plate member causes damage to either the cathode substrate 100 or the plate member of the envelope 101 during the heat treatment.
Furthermore, the conventional fluorescent display device is so constructed that the cathode substrate 100 on which the cathode 104 is arranged is formed separate from the envelope 101 on which the anode 103 is arranged. Such construction renders connection between each of electrode elements of the cathode 104 and a lead wire extending through a sealed section of the envelope 101 substantially hard. The connection is conventionally carried out by means of wire bondings 105. Unfortunately, this causes a disadvantage of failing to arrange the anode 103 and cathode 104 in proximity to each other because it is required to prevent a loop of a wire from contacting with each of the electrode elements.